JP4784650B2 - Encoding apparatus, target code amount adjustment method, and recording medium - Google Patents

Description

  The present invention relates to an encoding apparatus, a target code amount adjustment method, and a recording medium, and is applied to an image processing apparatus such as an encoder that encodes image data in accordance with an encoding method such as MPEG (Moving Picture Experts Group). Is preferred.

  Conventionally, image data is generally encoded by an encoder, recorded or distributed, and decoded by a decoder when the image is displayed. As shown in FIG. 1, in MPEG-2, for example, a GOP (Group Of Picture), which is a repeating unit of a picture, is formed for every 15 pictures.

  The MPEG-2 system has an I picture, a P picture, and a B picture. An I picture is generated by intra-picture encoding of pixel values as they are. The P picture is generated by performing forward predictive coding with reference to the previously appearing I picture and P picture. The B picture is generated by bi-directional predictive coding with reference to I and P pictures appearing before and after.

  Rate control for each picture in the MPEG-2 system is proposed in STEP 1 of TM (Test Model) 5. In STEP 1, in order to reduce the image quality difference in the GOP, the differential code amount between the GOP target code amount allowed for the GOP and the generated code amount of the encoded picture is stored in the virtual buffer. In STEP 1, a picture target code amount for a picture to be encoded is assigned according to the difference code amount and the picture type.

  In STEP 1, as shown in FIG. 1B, a large amount of code target code is allocated to the I picture and P picture used as the reference picture, and the B picture that does not become the reference picture has more than the I picture or P picture. A small picture target code amount is assigned (for example, see Patent Document 1).

JP 2008-78978 A

  By the way, the encoder having such a configuration is required to further improve the image quality of the bit stream.

  The present invention has been made in consideration of the above points, and intends to propose an encoding device capable of improving the image quality of a bitstream, a target code amount adjustment method, and a recording medium on which a target code amount adjustment program is recorded. It is.

  In order to solve this problem, in the encoding apparatus of the present invention, the encoding unit that encodes image data and the picture target code amount for each picture when encoding the image data are approximately equal for each type of picture. A calculation unit that calculates the image, a selection unit that selects an adjustment coefficient according to the position of the picture in the image processing unit among the adjustment coefficients in which the maximum value and the minimum value are repeated, and the picture target code calculated by the calculation unit An adjustment unit for adjusting the picture target code amount is provided by multiplying the amount by the adjustment coefficient selected by the selection unit.

  As a result, the encoding device can improve the picture quality of the picture corresponding to the local maximum value, while encoding the picture corresponding to the local minimum value with reference to the picture corresponding to the local maximum value. Deterioration can be suppressed.

In the encoding method of the present invention, the calculation step of calculating the picture target code amount when encoding the image data, and the adjustment coefficient in which the maximum value and the minimum value are repeated, are located at the position of the picture in the image processing unit. a selection step of selecting an adjustment coefficient corresponding, and the picture target code amount calculated by the calculating step by multiplying the adjustment coefficient selected by the selecting step, providing an adjustment step of adjusting the picture target code amount I did it.

  Thus, in the encoding method, the picture quality of the picture corresponding to the maximum value can be improved, while the picture corresponding to the minimum value can be encoded by referring to the picture corresponding to the maximum value. Deterioration can be suppressed.

Further, in the program recorded on the recording medium of the present invention, among the calculation step for calculating the picture target code amount when encoding the image data, and the adjustment coefficient in which the maximum value and the minimum value are repeated, in the image processing unit by multiplying a selection step of selecting an adjustment coefficient corresponding to the position of the picture, and the picture target code amount calculated by the calculation step, and an adjustment coefficient selected by the selecting step, adjusting for adjusting the picture target code amount Steps.

  As a result, the picture quality of the picture corresponding to the local maximum value can be improved, while the picture corresponding to the local minimum value can be encoded by referring to the picture corresponding to the local maximum value, thereby suppressing deterioration of the picture quality. Can do.

  According to the present invention, it is possible to improve the picture quality of a picture corresponding to a maximum value, while encoding a picture corresponding to a minimum value with reference to a picture corresponding to the maximum value. Degradation of image quality can be suppressed. Thus, the present invention can realize an encoding device, a target code amount adjustment method, and a recording medium on which a target code amount adjustment program is recorded, which can improve the image quality of the bitstream.

It is a basic diagram with which it uses for description of the rate control (1) by the conventional step 1. FIG. It is a basic diagram which shows the whole structure of an encoder. It is a basic diagram with which it uses for description of the rate control (2) by the conventional step 1. FIG. It is a basic diagram which shows the structure of a target bit rate calculation part. It is a basic diagram with which it uses for description of the rate control by 1st Embodiment. It is a basic diagram with which it uses for description of the problem of the conventional rate control. It is a basic diagram with which it uses for description of the improvement of the image quality between GOP by 1st Embodiment. It is a flowchart with which description of the target code amount adjustment processing procedure is provided. It is a basic diagram which shows the structure of the target bit rate calculation part by 2nd Embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The description will be given in the following order.
1. First embodiment (Details of rate control: I picture and P picture only)
2. Second embodiment (when B picture is included)
3. Other embodiments

<1. First Embodiment>
[1-1. Encoder configuration]
In FIG. 2, reference numeral 1 denotes an encoder as a whole. The encoder 1 includes an encoding unit 2 and a code amount control unit 3. The encoding unit 2 encodes image data supplied from the outside according to, for example, an MPEG (Moving Picture Experts Group) -2 system. The code amount control unit 3 brings the generated code amount of the image data (hereinafter referred to as a bitstream) encoded by the encoding unit 2 closer to the GOP target code amount set for each GOP (Group Of Picture). It is designed to control the rate.

  As shown in FIG. 3A, the encoder 1 generates a GOP that is an image processing unit including an I picture of one picture located at the head and a P picture continuing from the second to 14 pictures. An I picture is generated by intra-picture encoding of pixel values as they are. The P picture is generated by performing forward predictive coding with reference to the previously appearing I picture and P picture.

  When image data is supplied from an external device via the input terminal 10, the encoding unit 2 (FIG. 2) supplies the image data to the subtractor 11 and the prediction unit 12.

  When the reference image data is supplied from the prediction unit 12, the subtractor 11 generates difference information indicating a difference between the reference image data and the image data, and supplies the difference information to the orthogonal transform unit 13. On the other hand, when the reference image data is not supplied from the prediction unit 12, the subtractor 11 supplies the image data as it is to the orthogonal transformation unit 13 as difference information.

  The orthogonal transform unit 13 performs orthogonal transform processing such as DCT (Discrete Cosine Transform) on the difference information to generate an orthogonal transform coefficient, and supplies this to the quantization unit 14. When the quantization unit 14 quantizes the orthogonal transform coefficient while changing the quantization step based on the control of the code amount control unit 3 and generates a quantization coefficient, the quantization unit 14 converts the quantization coefficient into the inverse quantization unit 15 and the variable length coding unit. 16 is supplied.

  The inverse quantization unit 15 dequantizes the quantization coefficient to generate a local orthogonal transform coefficient, and supplies the local orthogonal transform coefficient to the inverse orthogonal transform unit 17. The inverse orthogonal transform unit 17 performs local orthogonal transform processing on the local orthogonal transform coefficient to generate local difference information, and supplies this to the adder 19.

  The adder 19 adds the temporally previous local image data and the difference information supplied from the prediction unit 12 to generate current local image data, and stores the current local image data in the image memory unit 18.

  The prediction unit 12 extracts a motion vector from the image data and the current local image data, performs a motion compensation process on the image data, and supplies this to the subtractor 11 as reference image data.

  The variable length encoding unit 16 generates a bit stream by performing variable length encoding on the quantization coefficient supplied from the quantization unit 14 according to the code table, supplies the bit stream to the code amount control unit 3, and outputs the output terminal 18. Output to an external device.

  The code amount control unit 3 is configured to calculate a quantization step used by the quantization unit 14 based on the code amount of the bit stream supplied from the variable length coding unit 16.

  The code amount control unit 3 supplies the bit stream supplied from the variable length encoding unit 16 to the excess / deficiency code amount calculation unit 21.

  The excess / deficiency code amount calculation unit 21 sets a GOP target code amount based on a preset GOP basic code amount. The excess / deficiency code amount calculation unit 21 calculates a difference code amount with respect to a GOP target code amount of a code amount of a coded bitstream in GOP units (hereinafter referred to as a GOP generated code amount), and the difference code The amount is supplied to the code distribution rate calculation unit 23.

  When the code distribution rate calculation unit 23 calculates the GOP target code amount for the next GOP by adding the difference code amount supplied from the excess / deficiency code amount calculation unit 21 to the GOP basic code amount, the GOP target code amount Is supplied to the target bit rate calculation unit 24 and the excess / deficiency code amount calculation unit 21. As a result, the GOP target code amount for the next GOP is set in the excess / deficiency code amount calculation unit 21.

  The target bit rate calculation unit 24 calculates a target bit rate for the next GOP based on the GOP target code amount supplied from the code distribution rate calculation unit 23.

  Further, the target bit rate calculation unit 24 quantizes the adjustment target code amount when executing a target code amount adjustment process (details will be described later) for calculating an adjustment target code amount for each picture based on the target bit rate. It supplies to the step calculation part 25.

  When the bit stream for each picture is supplied from the variable length coding unit 16, the excess / deficiency code amount calculation unit 21 calculates the bit stream code amount of the picture from the set GOP target code amount (hereinafter referred to as “picture”). The generated code amount S) is subtracted, and the remaining code amount R is calculated according to the following equation. The picture generation code amount S includes the generation code amounts of all picture types in the GOP.

  The excess / deficiency code amount calculation unit 21 supplies the picture generation code amount S and the remaining code amount R to the target bit rate calculation unit 24. The excess / deficiency code amount calculation unit 21 supplies the generated code amount for each macroblock to the quantization step calculation unit 25.

  The target bit rate calculation unit 24 executes target code amount adjustment processing for calculating an adjustment target code amount based on the target bit rate, the picture generation code amount S, and the remaining code amount R (details will be described later). The adjustment target code amount is supplied to the quantization step calculation unit 25.

  The quantization step calculation unit 25 performs a quantization step based on the adjustment target code amount supplied from the target bit rate calculation unit 24 and the generated code amount for each macroblock so that the picture generation code amount S approaches the adjustment target code amount. Is calculated. The quantization unit 14 generates a quantization coefficient using the quantization step.

  In this way, the encoder 1 calculates the adjustment target code amount by the code amount control unit 3 and performs quantization based on the adjustment target code amount, so that the picture generation code amount becomes the adjustment target code amount. So that the bitstream is generated. The encoder 1 performs rate control so that the GOP generated code amount approaches the GOP target code amount by calculating the adjusted target code amount based on the picture generated code amount by a target code amount adjusting process described later. .

[1-2. Picture target code amount adjustment process]
Next, target code amount adjustment processing executed by the target bit rate calculation unit 24 according to the target code amount adjustment program will be described. The target bit rate calculation unit 24 calculates the adjustment target code amounts (adjustment target code amounts Ti and TpC) for each picture based on the STEP 1 of TM5 in the MPEG (Moving Picture Experts Group) -2 system. .

  Specifically, the target bit rate calculation unit 24 calculates the picture target code amount Ti and the code amount S and the remaining code amount R supplied from the excess / deficiency code amount calculation unit 21 based on the calculated target bit rate. Tp is calculated. In STEP 1 of TM5, assuming that the picture generation code amount S for each picture is constant for each type of picture, the picture target code amount is assigned almost equally to each type of picture.

  As shown in FIG. 4, the picture type determination unit 31 of the target bit rate calculation unit 24 determines the picture type (I picture or P picture) and the picture number of the processing target picture for which the target code amount is to be calculated. When the processing target picture is an I picture, the picture type determination unit 31 supplies the target bit rate to the I picture target code amount calculation unit 32.

The I-picture target code amount calculation unit 32 calculates the parameter Xi according to the equation (2) and calculates the picture target code amount Ti according to the equation (3). Then, the I-picture target code amount calculation unit 32 supplies the picture target code amount Ti to the adjustment coefficient selection unit 35. Note that bitrate is the target bit rate, and Np and Nb are the numbers of P pictures and B pictures that have not yet been encoded in the GOP. In the present embodiment, since no B picture exists, the term Nb is always “0”.

When the processing target picture is a P picture, the picture type determination unit 31 uses the target bit rate, the picture generation code amount S and the remaining code amount R, and the determined picture number as the P code target code amount calculation unit 34. To supply.

  The P picture target code amount calculation unit 34 calculates the parameter Xp according to the equation (4) and calculates the picture target code amount Tp according to the equation (5).

  Note that the calculation method of the picture target code amounts Ti, Tp, and Tb is described in Non-Patent Document 1 below.

The Institute of Television Engineers of Japan Vol.49, No.4 (1995)

  Here, as shown in FIG. 3B, the P picture target code amount calculation unit 34 calculates the picture target code amount Tp so that the code amount is equally allocated to all the P pictures as in the conventional encoder. is doing.

  The adjustment coefficient selection unit 35 stores an adjustment coefficient in which the maximum value and the minimum value are repeated by repeating the increase and decrease for each picture as the picture number (that is, the position of the picture in the GOP) follows. . The adjustment coefficient selection unit 35 selects an adjustment coefficient according to the picture number and supplies the adjustment coefficient together with the picture target code amounts Ti and Tp to the picture target code amount adjustment unit 36.

  Specifically, as shown in FIG. 5B, the adjustment coefficient selection unit 35 sets “1” for the picture target code amount Tp of even picture numbers 2, 4, 6, 8, 10, 12, and 14. .5 "is selected. The adjustment coefficient selection unit 35 selects an adjustment coefficient based on “0.5” for the picture target code amount Tp of odd-numbered picture numbers 3, 5, 7, 9, 11, and 13.

  However, the adjustment coefficient selection unit 35 selects an adjustment coefficient of “1.0” for the picture target code amount Tp of the last picture number 15 in the GOP in order to use the GOP target code amount without leaving. . Similarly, the adjustment coefficient selecting unit 35 selects an adjustment coefficient of “1.0” for the picture target code amount Ti of the first I picture.

  That is, the adjustment coefficient selection unit 35 repeats increments and decrements every other time, and selects the adjustment coefficient so that the maximum value is obtained at even picture numbers and the minimum value is taken at odd picture numbers.

  The picture target code amount adjustment unit 36 multiplies the picture target code amounts Ti and Tp by the adjustment coefficient selected by the adjustment coefficient selection unit 35 to calculate an adjustment target code amount TpC. The picture target code amount adjustment unit 36 supplies the adjustment target code amount TpC to the excess / deficiency code amount calculation unit 21.

Specifically, the picture target code amount adjustment unit 36 adjusts the adjustment coefficient of “1.5” with respect to the picture target code amount Tp of picture numbers 2, 4, 6, 8, 10, 12, and 14 that are even numbers. And the multiplication value is set as the adjustment target code amount TpC. Picture for the target code amount adjusting unit 3 6, with respect to the picture target code amount Tp of the picture numbers 3,5,7,9,11,13 made odd, multiplied by the adjustment coefficient relative to the "0.5" The multiplication value is set as the adjustment target code amount TpC.

  Also, the picture target code amount adjustment unit 36 multiplies the picture code amounts Ti and Tp of the picture numbers 1 and 15 by “1.0”, and sets the multiplied values as the adjustment target code amounts TiC and TpC. If the adjustment coefficient is “1.0”, the picture target code amount adjustment unit 36 may use the picture target code amounts Ti and Tp as they are as the adjustment target code amounts TiC and TpC without multiplication by the adjustment coefficient. good.

  As a result, as shown in FIG. 5C, the adjustment target code amount TpC repeatedly increases and decreases for each picture.

  At this time, in the P picture having an even picture number, the image quality can be improved as the adjustment target code amount TpC increases. In addition, in a P picture having an odd picture number, by referring to a P picture with improved image quality, it is possible to reduce image quality deterioration more than the code amount decrease amount. As a result, the picture target code amount adjustment unit 36 can improve the image quality as the GOP total as compared with the conventional method that does not multiply the adjustment coefficient.

  In addition, it is known that when an image with good image quality and an image with poor image quality are repeated, an image with good image quality is recognized by human being preferentially recognized. Therefore, the picture target code amount adjusting unit 36 can allow the user to recognize the image quality better than the actual image quality when displaying the decoded image data obtained by decoding the bitstream on the display device.

  Here, as shown in FIG. 6, the conventional encoder assigns the largest picture target code amount to the I picture. For this reason, when displaying the decoded image data, the conventional encoder has made the image quality extremely good every time an I picture appears, giving the user the impression that the screen has been switched. .

  The picture target code amount adjustment unit 36 increases the adjustment target code amount TpC of the P picture immediately after the I picture (that is, the picture number “2”). Thereby, the picture target code amount adjustment unit 36 can improve the image quality of the picture immediately after the I picture.

  The picture target code amount adjustment unit 36 increases the adjustment target code amount TpC immediately before the last P picture of the GOP (that is, the picture number “14”). As a result, the picture target code amount adjustment unit 36 can improve the image quality of the last P picture (that is, picture number “15”) in which the next I picture appears.

  That is, the picture target code amount adjustment unit 36 can improve the image quality of two pictures immediately before the I picture and one picture immediately after the I picture. As a result, as shown in FIG. 7, the picture target code amount adjustment unit 36 can smoothly connect the GOPs and does not make only the I picture stand out, thereby improving the image quality of the decoded image data as a whole. Has been made to get.

  Furthermore, the picture target code amount adjustment unit 36 uses “0.5” as a reference, and the picture numbers 3, 5, 7, 9, 11, 13 that are odd numbers so that the value gradually increases toward the end of the GOP. The adjustment factor corresponding to is selected.

  Specifically, the picture target code amount adjustment unit 36 applies 0.523, 0.523, 0.531, and 0.523, 0.523, 0.531, to the picture target code amounts Tp of odd-numbered picture numbers 3, 5, 7, 9, 11, and 13. Multiply by the adjustment coefficients of 0.539, 0.555, and 0.602.

  As a result, the picture target code amount adjustment unit 36 can gradually improve the image quality as it moves after the GOP, so that the image quality of the latter half of the GOP, in which the image quality is likely to deteriorate due to propagation of an error due to reference, can be improved. Can do. For this reason, the picture target code amount adjustment unit 36 can equalize the image quality in the first half part and the second half part, and can smoothly connect the GOPs.

  The series of target code amount adjustment processes described above can be executed by hardware or can be executed by software. When the target code amount adjustment processing is realized by software, a target bit rate calculation unit 24 is virtually formed in a CPU (Central Processing Unit) and a RAM (Random Access Memory). Then, the target code amount adjustment processing is executed by expanding the variable length decoding program stored in the ROM into the RAM.

  In this way, the target bit rate calculation unit 24 calculates the picture target code amount Tp so that the picture quality for each picture becomes equal. Then, the target bit rate calculation unit 24 multiplies the target bit number by the adjustment coefficient corresponding to the picture number so as to repeat the increase and decrease, and calculates the adjustment target code amount TpC.

  Thus, the target bit rate calculation unit 24 can generate a P picture with an odd picture number with a small code amount by referring to a P picture with an even picture number with a large code amount. Therefore, the target bit rate calculation unit 24 can improve the image quality of the P picture with the even picture number while suppressing the deterioration of the image quality in the P picture with the odd picture number, and improve the image quality as the GOP overall. It is made to be able to let you.

[1-3. Specific processing procedure]
Next, the target code amount adjustment processing executed according to the target code amount adjustment processing procedure RT1 will be described with reference to the flowchart of FIG.

  When the picture generation code amount and the remaining code amount are supplied from the excess / deficiency code amount calculation unit 21, the target bit rate calculation unit 24 starts the target code amount adjustment processing procedure RT1, and proceeds to step SP1.

  In step SP1, the target bit rate calculation unit 24 determines whether or not the processing target picture is an I picture. Here, if a positive result is obtained, the target bit rate calculation unit 24 proceeds to the next step SP2 because the processing target picture is an I picture.

  In step SP2, when the target bit rate calculation unit 24 calculates the picture target code amount Ti for the I picture according to the equations (2) and (3), the process proceeds to an end step and ends the target code amount adjustment processing procedure RT1. .

  On the other hand, if a negative result is obtained in step SP1, the target bit rate calculation unit 24 proceeds to the next step SP3 because the processing target picture is a P picture.

  In step SP3, the target bit rate calculation unit 24 calculates the picture target code amount Tp for the P picture according to the equations (4) and (5) while updating the remaining code amount R according to the equation (1). The process proceeds to step SP4.

  In step SP4, when the target bit rate calculation unit 24 selects an adjustment coefficient corresponding to the picture number from among the adjustment coefficients that repeat the maximum value and the minimum value in the order of the picture numbers, the process proceeds to the next step SP5.

  In step SP5, the target bit rate calculation unit 24 calculates the adjustment target code amounts TiC and TpC by multiplying the picture target code amounts Ti and Tp calculated in step SP3 by the adjustment coefficient corresponding to the picture number. The process proceeds to an end step to end the target code amount adjustment processing procedure RT1.

[1-4. Operation and effect]
In the above configuration, the encoder 1 calculates a picture target code amount Tp that is a picture target code amount when encoding image data. The encoder 1 selects an adjustment coefficient corresponding to the position of a picture (that is, a picture number) in a GOP that is an image processing unit from among adjustment coefficients in which the maximum value and the minimum value are repeated by increasing / decreasing for each picture. The encoder 1 adjusts the picture target code amount Tp by multiplying the picture target code amount Tp by the selected adjustment coefficient, and calculates the adjustment target code amount TpC.

  As a result, the encoder 1 generates a bitstream so that the code amount repeatedly increases and decreases, and alternately generates a picture with a large code amount and a picture with a reduced code amount. Since the encoder 1 improves the image quality of a picture with a large code amount, and encodes a picture with a reduced code amount by referring to a picture with an improved image quality, it suppresses deterioration of the image quality in the picture with the reduced code amount. can do. Therefore, the encoder 1 can improve the image quality as a GOP total.

  The encoder 1 calculates the picture target code amount Tp so as to be almost equal for each type of picture. Thus, the encoder 1 can set the adjustment target code amount TpC to repeat the maximum value and the minimum value, and therefore encodes the image data so that the picture code amounts Ti and Tp repeat the maximum value and the minimum value. can do.

  The encoder 1 selects an adjustment coefficient having a value larger than 1 for a picture to be encoded after the I picture.

  As a result, the encoder 1 can improve the image quality of the picture immediately after the I picture to which the most code amount is assigned, and therefore naturally connects subsequent low-quality pictures without making the I picture stand out. be able to.

  The encoder 1 calculates the picture target code amount Tp so that the bit stream code amount becomes the GOP target code amount set for each GOP, and selects an adjustment coefficient of 1 for the last picture in the GOP. .

  As a result, the encoder 1 can assign all the remaining code amounts obtained by subtracting the code amount of the already encoded bitstream from the GOP target code amount as the adjustment target code amount Tp, leaving no surplus code amount. You can

  The encoder 1 selects an adjustment coefficient having a value larger than 1 for the picture immediately before the last picture in the GOP (that is, picture number 14).

  As a result, the encoder 1 can encode the last picture in the GOP with reference to a picture with good image quality, and can improve the image quality of the two pictures immediately before the I picture that comes first in the next GOP.

  As a result, the encoder 1 can improve the picture quality of the picture immediately before the I picture to which the most code amount is assigned, so that the GOPs can be smoothly connected without making the I picture stand out.

  The encoder 1 selects the adjustment coefficient so that the value increases as the position of the picture in the GOP moves backward (that is, as the picture number increases).

  Thereby, the encoder 1 can gradually improve the picture quality of the picture toward the next GOP in which the I picture appears, and can connect the GOPs more smoothly.

  The GOP is composed of an I picture and a P picture. As a result, since all the pictures are referred to, the encoder 1 ensures the relationship of encoding pictures with a reduced code amount by referring to pictures with improved image quality, and fully exhibits the effects of the present invention. can do.

  According to the above configuration, the encoder 1 sets the adjustment target code amount so that the code amount for each picture in the bitstream repeatedly increases and decreases in the GOP. The encoder 1 encodes the image data so that the bitstream code amount for the picture becomes the adjustment target code amount.

  Thereby, the encoder 1 can bring the picture quality of a picture with a large code amount closer to that of an I picture and improve the picture quality of every other picture. That is, when displaying the decoded image, the encoder 1 makes the user feel as if the image quality of the entire decoded image data is improved by causing only the image with improved image quality to appear periodically. Can do. Thus, the present invention can realize a coding apparatus, a target code amount adjustment method, and a recording medium on which a target code amount adjustment program is recorded that can improve image quality.

[2. Second Embodiment]
In 2nd Embodiment, as shown in FIG. 9, the same code | symbol is attached | subjected and shown to the location corresponding to 1st Embodiment shown in FIGS. The second embodiment is different from the first embodiment in that a GOP includes a B picture in addition to an I picture and a P picture. Further, the second embodiment is different from the first embodiment in that an adjustment coefficient selection unit and a target code amount adjustment unit respectively corresponding to an I picture, a P picture, and a B picture are provided.

  As shown in FIG. 9, when the processing target picture is an I picture, the I-picture target code amount calculation unit 32 of the target bit rate calculation unit 50 generates the picture target code amount Ti according to the equation (2). This is supplied to the adjustment coefficient selection unit 35A for I picture. Nb is the number of unencoded B pictures, Kb is the ratio of the quantization scale corresponding to the B picture, and Kb = 1.4.

  The I picture adjustment coefficient selection unit 35A selects the adjustment coefficient “1.0” corresponding to the picture number, and supplies the adjustment coefficient to the I picture target code amount adjustment unit 36A. The I-picture target code amount adjustment unit 36A generates the adjustment target code amount TiC by multiplying the picture target code amount Ti by the adjustment coefficient “1.0”.

In addition, the P picture target code amount calculation unit 34 generates the picture target code amount Tp according to the equations (4) and (5). The P picture target code amount adjustment unit 36B multiplies the adjustment coefficient selected in accordance with the picture number by the P picture adjustment coefficient selection unit 35B to calculate the adjustment target code amount Tp C.

  The B picture target code amount calculation unit 51 calculates the B picture target code amount Tb for the first B picture in the GOP according to the equations (6) and (7).

  The B picture target code amount adjustment unit 36C multiplies the B picture target code amount Tb by the adjustment coefficient selected according to the picture number by the B picture adjustment coefficient selection unit 35C to generate the adjustment target code amount TbC. To do.

  As a result, the adjustment target code amounts TiC, TpC, and TbC are supplied to the excess / deficiency code amount calculation unit 21.

As described above, the target bit rate calculation unit 50 adjusts the adjustment coefficient larger than 1 for the picture target code amount Tp and the B picture target code amount Tb having an even picture number among the pictures other than the first and last pictures in the GOP. To generate adjustment target code amounts TpC and TbC. Target bit rate calculation unit 5 0 multiplies less than 1 adjustment coefficient for the picture of the picture number is odd, to generate an adjusted target amount of code TpC and TBC.

  Thereby, the target bit rate calculation unit 50 can repeat the increase and decrease of the picture target code amount for the pictures other than the first and last in the GOP, as in the first embodiment, and the image quality as the GOP total can be reduced. Can be improved.

[3. Other Embodiments]
In the first and second embodiments described above, the target bit rate calculation unit 24 calculates the picture target code amount Tp so as to be approximately equal for each type of picture. The target bit rate calculation unit 24 multiplies the adjustment coefficient corresponding to the position of the picture (that is, the picture number) in the GOP, which is the image processing unit, and the picture target code amount Tp among the adjustment coefficients in which the maximum value and the minimum value are repeated. To do. Thus, the case where the target bit rate calculation unit 24 adjusts the picture target code amount Tp and calculates the adjusted target code amount TpC has been described. The present invention is not limited to this. For example, the picture target code amount may be calculated according to the complexity of the image, and the picture target code amount may be multiplied by the adjustment coefficient. Further, the adjustment target code amount TpC may be calculated such that the maximum value and the minimum value are directly repeated without calculating the picture target code amount Tp.

  In the first and second embodiments described above, a case has been described in which an adjustment coefficient larger than 1 is selected for a picture encoded after an I picture. The present invention is not limited to this. In short, the adjustment target code amount for each picture may be increased or decreased, and an adjustment coefficient smaller than 1 may be selected.

  Further, in the above-described first and second embodiments, the case where the GOP is configured by 15 pictures having an odd GOP has been described, but the present invention is not limited to this. The present invention is not limited to the number of pictures constituting a GOP, and the number of the pictures may be an odd number or an even number.

  Further, in the above-described first and second embodiments, the case where the image processing unit is the GOP unit has been described. The present invention is not limited to this, and various other units can be used as image processing units.

  Further, in the first and second embodiments described above, the case where the picture target code amount Tp is calculated in accordance with the STEP 1 of TM5 in MPEG-2 has been described. The present invention is not limited to this, and the picture target code amount Tp may be calculated by various other methods.

  Furthermore, in the first and second embodiments described above, the case has been described where the picture immediately before the last picture in the GOP is multiplied by an adjustment coefficient larger than 1. The present invention is not limited to this. In short, the adjustment target code amount for each picture may be increased or decreased, and an adjustment coefficient smaller than 1 may be multiplied.

  Furthermore, in the first and second embodiments described above, the case has been described in which the minimum value of the adjustment coefficient smaller than 1 increases as the position of the picture in the GOP moves backward. The present invention is not limited to this. For example, the value of the adjustment coefficient is increased while increasing or decreasing from the center of the GOP toward the front and rear directions, or the value of the adjustment coefficient is the same between the maximum value and the minimum value. You may do it. In the present invention, the adjustment coefficient may be increased similarly for the maximum value.

  Further, in the above-described embodiment, the case where the target code amount adjustment program or the like is stored in advance in a ROM or a hard disk drive has been described. However, the present invention is not limited to this, and the memory stick (registered by Sony Corporation) is described. It may be installed in a flash memory or the like from an external storage medium such as a trademark. In addition, a target code amount adjustment program or the like is transmitted via a wireless local area network (USB) such as USB (Universal Serial Bus) or Ethernet (registered trademark) (registered trademark) 802.11a / b / g. It may be acquired from the outside and further distributed by terrestrial digital television broadcasting or BS digital television broadcasting.

  Further, in the above-described first and second embodiments, the case where the present invention is applied to the encoder 1 conforming to MPEG-2 has been described. The present invention is not limited to this, and can be applied to encoders of various methods. The present invention can be applied to, for example, an encoder compliant with MPEG-4, AVC (Advanced Video Coding), VC-1 standardized on Windows (registered trademark) Media Video 9, JPEG (Joint Photographic Experts Group), or the like. .

  Furthermore, in the first embodiment described above, the encoding unit 2 as an encoding unit, the P picture target code amount calculation unit 34 as a calculation unit, the adjustment coefficient selection unit 35 as a selection unit, The case where the encoder 1 as the encoding device is configured by the target code amount adjustment unit 36 as the adjustment unit has been described. The present invention is not limited to this, and an encoding device of the present invention may be configured by an encoding unit, a calculation unit, a selection unit, and an adjustment unit having various other configurations.

  The encoding apparatus of the present invention can be used for an information processing terminal that executes image compression processing, for example.

  DESCRIPTION OF SYMBOLS 1 ... Encoder, 2 ... Encoding part, 3 ... Code amount control part, 10 ... Input terminal, 11 ... Subtractor, 14 ... Quantization part, 21 ... Excess / deficiency code amount calculation part, 23 ... Code distribution amount calculation unit, 24... Target bit rate calculation unit, 25... Quantization step calculation unit, Ti... Picture target code amount TiC, TpC, TbC ... Adjustment target code amount, Tp. Target code amount, Tb: B picture target code amount.

Claims (10)

An encoding unit for encoding image data;
A calculation unit that calculates a picture target code amount for each picture when encoding image data;
A selection unit that selects an adjustment coefficient according to the position of the picture in the image processing unit among adjustment coefficients in which the maximum value and the minimum value are repeated;
An encoding device comprising: an adjustment unit that adjusts the picture target code amount by multiplying the picture target code amount calculated by the calculation unit by the adjustment coefficient selected by the selection unit. The selection part
The encoding apparatus according to claim 1, wherein an adjustment coefficient larger than 1 is selected for a picture encoded after an I picture. The calculation unit is
Calculating the target code amount so that the code amount of the bitstream encoded by the encoding unit is the image processing unit target code amount set for each image processing unit;
The selection part
The encoding apparatus according to claim 2, wherein an adjustment coefficient of 1 is selected for the last picture in the image processing unit. The selection part
The encoding apparatus according to claim 3, wherein an adjustment coefficient larger than 1 is selected for a picture immediately before the last picture in the image processing unit. The selection part
The encoding apparatus according to claim 4, wherein the adjustment coefficient is selected so that the value increases as the position of the picture in the image processing unit advances backward. The calculation unit is
The encoding apparatus according to claim 5, wherein the picture target code amount is calculated so as to be substantially equal for each type of picture. The image processing unit is
The encoding apparatus according to claim 1, comprising an I picture and a P picture. The encoding unit is
The encoding apparatus according to claim 7, wherein the image data is encoded according to an MPEG-2 system. A calculation step of calculating a picture target code amount when encoding image data so as to be substantially equal for each type of picture;
A selection step of selecting an adjustment coefficient corresponding to the position of the picture in the image processing unit from among the adjustment coefficients in which the maximum value and the minimum value are repeated;
A target code amount adjustment method comprising: an adjustment step of adjusting the picture target code amount by multiplying the picture target code amount calculated by the calculation step by the adjustment coefficient selected by the selection step . Against the computer,
A calculation step of calculating a picture target code amount when encoding image data so as to be substantially equal for each type of picture;
A selection step of selecting an adjustment coefficient corresponding to the position of the picture in the image processing unit from among the adjustment coefficients in which the maximum value and the minimum value are repeated;
A target code amount adjustment program for executing the adjustment step of adjusting the picture target code amount by multiplying the picture target code amount calculated by the calculation step by the adjustment coefficient selected by the selection step Recording medium on which is recorded.

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